*picture* can anyone identify if this is a skin issue?

I'm not sure if this is a skin issue, callous, or just some generic crusties? 

Ducky has been having many un-identifiable health issues lately.  lameness, limping, loss of appetite, weight loss etc etc..  .    X-rays, bloodwork and general check's have turned up nothing.   Noticing she's limping on one paw in particular,  I checked it out and saw some of this crusty stuff ( which I have seen before but passed off as rough skin, like we'd get on our own feet)

she will let me rub her lame leg,  but cries in pain if I touch the pads of her paw or the "toe" (the useless one above her joint)  with the rough skin (cat anatomy anyone??)  some of this crust is present on several of her toes, but this one is the most prevalent.  

am I crazy or can this bit of rough skin tell me theres finally an identifiable issue..   

Sorry you kitty is going through this. Cats in pain will not eat and it sounds like she is extremely uncomfortable. I don't know what that is, but I'd get her back to the vet and have it checked. What did the vet do about her other issues?

Not seen anything like this before but it definitely doesn't look right and it sounds like Ducky is in a lot of pain as they tolerate so much before you are even aware of it usually. I'd get her back to the vet ASAP. What a shame. I hope your vet is now able to identify what's going on and find a way to resolve her pain.